On 2022-11-02 10:58, Christian König wrote:
It can happen that we query the sequence value before the callback
had a chance to run.
Work around that by grabbing the fence lock and releasing it again.
Should be replaced by hw handling soon.
kfd_flush_tlb is always called after waiting for map/unmap to GPU fence
signalled, that means the callback is already executed and the sequence
is increased if tlb flush is needed, so no such race from KFD.
I am not sure but seems the race does exist for amdgpu to grab vm and
schedule job.
Acked-by: Philip Yang <Philip.Yang@xxxxxxx>
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index 9ecb7f663e19..e51a46c9582b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -485,6 +485,21 @@ void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct seq_file *m);
*/
static inline uint64_t amdgpu_vm_tlb_seq(struct amdgpu_vm *vm)
{
+ unsigned long flags;
+ spinlock_t *lock;
+
+ /*
+ * Work around to stop racing between the fence signaling and handling
+ * the cb. The lock is static after initially setting it up, just make
+ * sure that the dma_fence structure isn't freed up.
+ */
+ rcu_read_lock();
+ lock = vm->last_tlb_flush->lock;
+ rcu_read_unlock();
+
+ spin_lock_irqsave(lock, flags);
+ spin_unlock_irqrestore(lock, flags);
+
return atomic64_read(&vm->tlb_seq);
}
